Like other email service providers AOL also use SMTP protocol for sending emails and use Mail User Agent(MUA) to distribute emails to the recipients. Now SMTP server may get disturbed due to incorrect settings for email clients. Clearly, it will create issues for you in sending and receiving emails. You need to fix the issue to resume the AOL service. Contact at AOL support and get fixed. There you can get expert support with the professional approach of the solution. An easy approach to review the settings and alter the incorrect changes will surely be fixing your issues.